The present invention relates to a system for smoothing of spreading transitions between image regions included in television signals to be transmitted which are processed in a still picture signal processing method and a motion picture signal processing method, and particularly to a circuit for accurately detecting a motion signal which represents a moving image, so as to control the transitions between image regions of a frequency-unfolded image signal.
Standard television system such as an NTSC or a PAL system, which represent images, processes a television signal adaptively in accordance with an amount of motions of the signal. This adaptive processing of the signal may result in quasi-motion picture regions between image regions being processed in a still picture signal processing method and other image regions being processed in a motion picture signal processing method. If differences in the processing methods are perceived and, the different regions and the transition between them are discerned by a viewer, image quality is degraded.
For example, for the purpose of separating chrominance and luminance components from a composite video signal, a frame comb filter or a line comb filter may be used. As long as there is no change in the image signal at frame time intervals, when separating chrominance and luminance components from the composite video signal using the frame comb filter, the luminance and chrominance components can be completely separated. If the scene changes, however, over the frame time intervals, then some color information will be present in the separated luminance component and some brightness information will be present in the chrominance component.
A line comb filter also used to separate the luminance and chrominance components from the composite video signal does not produce significantly degraded component signals in the presence of image motion. However, the line comb filter reduces the vertical resolution of the reproduced image in comparison with the frame comb filter. In addition, in locations where a vertical transition occurs, an image processed by the line comb filter may be degraded due to both color information introduced into the luminance component, producing an image artifact known as hanging dots and brightness information introduced into the chrominance, producing incorrect colors in the neighborhood of the transition.
Therefore the television signal is adaptively processed by detecting the presence or absence of image motion. In the regions in which the image is stationary, the frame comb filter is used, and in the regions in which the image is moving, the line comb filter is used.
Another example of such adaptive processing is an adaptive double-scanned, non-interlaced scan converter. In such a converter, interstitial lines are displayed between lines of the current field. However, the interstitial lines may be those transferred from the preceding field, in the presence of image changes producing visible artifacts such as serrated contours. The interstitial lines may also be interpolated from lines within the current field, but the vertical resolution is reduced and line flicker may occur. In regions in which image changes are detected, intrafield interpolated interstitial lines are displayed and field-delayed interstitial lines are displayed in other way.
Yet another example is an adaptive peaking circuitry in which regions having relatively high noise are processed with a relatively low peaking factor and regions having relatively low noise are processed with a relatively high peaking factor.
In all of the above examples, the television signals are processed adaptively in response to the values of estimated parameters of the image. The parameters are a motion in the case of luminance/chrominance separation and double scanning non-interlaced conversion, and a relative level of noise in the case of the peaking. Differently processed regions, and noticeable boundaries between regions where the parameter is present and those where it is absent are undesirable artifacts introduced by the above types of adaptive processing types.
U.S. Pat. No. 5,113,262 issued May 12, 1992, to Strolle et alii, entitled "AN IMPROVED VIDEO SIGNAL RECORDING SYSTEM" and assigned to Samsung Electronic Co., Ltd., describes a recording system for recording and reproducing a full bandwidth video signal on and from a recording medium having a limited bandwidth by folding the high frequency component of a luminance signal into the low frequency component of the luminance signal.
In U.S. Pat. No. 5,113,262 a motion signal which represents a moving image is recorded together with the folded luminance signal and the chrominance signal on the recording medium. The motion signal is used to control the transition between regions of the full bandwidth luminance signal which is unfolded into the original frequency bands when reproducing.
That is, in the previous work of the inventor and his co-workers, the high frequency component of the luminance signal is folded into the low frequency component of the luminance signal in recording. At this time, the high frequency component of the luminance signal is modulated by a folding carrier, so that the folded luminance signal has a phase difference of 180 degrees between frames, between scanning lines, and between pixels.
Accordingly, in reproducing, the high frequency component folded into the low frequency component of the folded luminance signal is demodulated by the unfolding carrier having the same phase and frequency as those of the folding carrier, so that the high frequency component of the luminance signal is unfolded to the original frequency band.
However, the folding carrier and the sideband thereof will be present in the unfolded luminance signal. The resultant luminance signal unfolded by the folding carrier and the sidebands thereof has a phase difference of 180 degrees between frames.
As a result, the conventional motion signal detecting circuit for detecting the level difference of pixels between fames as the motion signal, has difficulty in detecting accurately the motion signal from the unfolded luminance signal due to the phase off-set between frames.
More particularly, the unfolding procedure involves the heterodyning, or multiplicative mixing, of the folded-spectrum signal (or the folded-down portion thereof separated by comb filtering) with an unfolding carrier, the horizontal spatial frequency of which is located above the folded spectrum. This unfolding carrier acquires lower and upper sidebands from this multiplicative mixing procedure. The original high-frequency subspectrum, which appears in the folded-spectrum signal as a reversed-in-frequency subspectrum that occupies the same band as the original low-frequency subspectrum, mixes with the unfolding carrier to generate a lower sideband component that reproduces the original high-frequency subspectrum without spectrum reversal. There is also a higher sideband component which reproduces the reversed-in-frequency subspectrum as translated up in frequency, which product of the unfolding procedure can be suppressed by lowpass filtering or bandreject filtering.
In practice, since the folded-spectrum signal is descriptive of both image portions that change from frame to frame and image portions that do not change from frame to frame, separating the folded-down portion of the folded-spectrum signal by comb filtering cannot be done without previously generating a motion signal indicative of frame-to-frame change in the signal prior to its having been folded. As noted previously, such a motion signal cannot be determined from the folded-spectrum signal using highpass frame comb filtering, because in the folded-spectrum signal the frame-to-frame reversal of phase in the folded-down high frequency subspectrum is indistinguishable from frame-to-frame change in the signal prior to its having been folded. U.S. patent application Ser. No. 07/569,029 describes an unfolding procedure in which the complete folded-spectrum signal is mixed with the (un)folding carrier. Then, the resulting product is vertically lowpass filtered to generate an unfolded high-frequency subspectrum that is added back to the complete folded-spectrum signal. In the unfolded signal that results from this additive combining, the low-frequency subspectrum is still accompanied by an overlapping folded-high-frequency subspectrum. Since it is an in-band artifact of unfolding, removal of this undesirable reversed-in-frequency subspectrum cannot be done by the lowpass filtering or bandreject filtering of the prior art.
When the complete folded-spectrum signal is mixed with the (un)folding carrier to generate an unfolded high-frequency subspectrum, there are other undesirable products of the unfolding procedure that arise from the original low-frequency subspectrum multiplicatively mixing with the unfolding carrier. These products exhibit frame-to-frame anti-correlation, so they must be suppressed in signal supplied to a motion detector, or they will be detected to give spurious indications of frame-to-frame image motion. There is an additional upper sideband component of the unfolding carrier, which reproduces the original low-frequency subspectrum as translated up in frequency, and this undesirable product of the unfolding procedure can also be suppressed by lowpass filtering or bandreject filtering. Another undesirable product of the unfolding procedure is an additional lower sideband component of the unfolding carrier which is a reversed-in-frequency subspectrum generated as the difference between the original low-frequency subspectrum and the unfolding carrier. When the horizontal spatial frequency of the folding and unfolding carriers is not much above the uppermost frequency in the original high-frequency subspectrum, this reversed-in-frequency subspectrum occupies the same horizontal-spatial-frequency band as the reproduction of the original high-frequency subspectrum without spectrum reversal. Since it is an in-band artifact of unfolding, removal of this undesirable reversed-in-frequency subspectrum cannot be done by the lowpass filtering or bandreject filtering of the prior art.
The problem of removing the reversed-in-frequency subspectra that are undesirable in-band artifacts of unfolding is solved by applicant and his co-inventors in their U.S. patent application Ser. No. 07/562,907 filed Aug. 6, 1990; entitled "APPARATUS FOR ELIMINATING THE FOLDING CARRIER AND SIDEBANDS FROM THE UNFOLDED VIDEO SIGNAL" and assigned to Samsung Electronics Co., Ltd., which U.S. application corresponds to Korean patent application 90-17610.